In recent years, as a transition technique to the fourth-generation mobile communication system, attention is focused on a 3G/WLAN inter-working technique that, by combining the current third-generation mobile communication system with WLAN, provides to users a wide range communication area of the third-generation mobile communication system and a wideband access of a WLAN system. In addition, a seamless handover technique is proposed which enables users to move between 3G and WLAN without taking into account the difference between wireless access schemes (for example, Non-Patent Document 1).
When a communication terminal apparatus receiving services in the third-generation mobile communication network moves to a WLAN area and thereby performs a handover to switch communication using the third-generation mobile communication system to communication using WLAN, the communication terminal apparatus detects an access point of WLAN prior to the handover. FIG. 1 shows a conventional access point detection period. In FIG. 1, the horizontal axis is time. As shown in FIG. 1, the communication terminal apparatus detects an access point at regular period T10 during communication using the third generation mobile communication system such as a call according to FOMA (registered trademark). The communication terminal apparatus detects an access point at time t2 by moving into the WLAN area at time t1. The communication terminal apparatus detects an access point, thereby performing a handover at time t3. Then, at t3 and after when the handover is finished, the communication terminal apparatus stops a call using the third-generation mobile communication system, and then, performs a call using WLAN. A time from time t1 at which the communication terminal apparatus has moved into the WLAN area to time t3 at which the handover is performed, is defined as a “handover time.” Further, the communication terminal apparatus does not detect an access point during a call using WLAN at t3 and after.
Non-patent Document 1: “WLAN-GPRS integration for next-generation mobile data networks,” Apostolis K. Salkantzis, Chad Fors and Rajesh Pazhyannur, IEEE Wireless Communications, vol. 9, no. 5 October 2002, pp. 112-124.